Robotically loaded epitaxial deposition apparatus

ABSTRACT

A susceptor carrying semiconductor wafers for processing is suspended from a compliant attachment at its upper end and is lowered into a reaction chamber for processing. At the completion of processing, the susceptor is withdrawn vertically to permit a robot to unload the processed wafers and load unprocessed wafers. In order to fix the position of the susceptor during the loading operations, a support carriage is moved into position to engage the lower end of the susceptor. Noxious and corrosive chloride vapors are simultaneously withdrawn from the reaction chamber by a vacuum line attached to the support carriage.

This is a division of application Ser. No. 07/354,161 filed May 19,1989, pending.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of silicon waferfabrication equipment useful in the manufacture of semiconductordevices, more particularly to apparatus for depositing an epitaxiallayer from a source gas by the chemical vapor deposition (CVD) method,and especially to improvements in such apparatus when used with roboticloading of wafers.

Apparatus of the above type is used in the fabrication of semiconductordevices on 100 millimeter or larger wafers of silicon. Epitaxial layersare formed on the surfaces of the wafers by heating them to temperaturesin the region of 1100 to 1200 degrees Celsius in a bell jar containing agaseous atmosphere consisting of a hydrogen carrier gas mixed with oneor more reactive gases such as a silicon source gas or a dopant sourcegas.

In order to provide automatic processing of a large number of wafers, arobotic loader, together with the necessary control electronics, can beused to automatically load unprocessed wafers onto the susceptor whichis used to support them. The susceptor is then loaded into the reactionchamber, processing is carried out, and the susceptor is removed fromthe reaction chamber, whereupon the robot removes the processed wafersfrom the susceptor and loads unprocessed wafers.

DESCRIPTION OF THE PRIOR ART

The known prior art is exemplified by automated epitaxial reactorsystems of the type represented by the Model 7010 system supplied byApplied Materials of Santa Clara, Calif. This system uses a roboticloader to load and unload substrates from the susceptor.

The geometry and size of this system permit supporting the susceptorquite rigidly from its base. When the susceptor is withdrawn from thebell jar or reaction chamber to permit operation of the roboticsubstrate loader, a stream of filtered air sweeps over the susceptorsurface to remove corrosive vapors such as chlorides which arebyproducts of the CVD process.

Although this system performs well, it was desired to develop anautomated system in which the susceptor is supported from a single pointnear its upper end by a suspension mount which provides sufficientcompliance to permit the susceptor to center itself below the mountthrough gravitational force alone. In this regard, it will be understoodthat the words "compliance" and "compliant", when used in thisapplication with respect to the susceptor mounting of the presentinvention, denote that flexibility of the mounting which permits thesusceptor to swing slightly from side to side in the same manner as ifthe susceptor were hung from a rope. Such a mounting causes somedifficulty during the operation of the robotic loader, since thecompliance of the mount permits unwanted movement of the susceptorduring loading.

Further, although the filtered air stream of the prior art automatedsystem removed virtually all of the corrosive vapor and particulatecontaminants, further improvements in this regard are always considereddesirable.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an automated epitaxialreactor system having a greater capacity than the prior art systems.

A further object of the present invention is to provide such a system inwhich the efficiency of removal of harmful process byproducts isenhanced.

A further object of the present invention is to provide such a systemwith a self-centering susceptor for supporting substrates.

A further object of the present invention is to provide such a systemwith a means to support and fix the position of the susceptor duringsubstrate loading operations.

A further object of the present invention is to provide such a systemwith a means to catch a substrate which is accidentally dropped duringthe operations of loading or unloading substrates, and to therebyprevent damage to the system.

A further object of the present invention is to provide such a systemhaving a susceptor stabilization means in a form which can be extendedtoward the susceptor at the start of substrate loading and withdrawn atthe end of substrate loading.

A further object of the present invention is to provide such a system inwhich susceptor stabilization and removal of harmful process byproductsis accomplished by a single movable element.

To the above ends, an automated epitaxial vapor deposition apparatusaccording to the present invention uses an elongated, multisidedsusceptor which is suspended by a centrally located gimballed mountingat its top end. The susceptor has sufficient axial length to accommodatetwo or more substrates on each of its sides.

The susceptor is lowered into a bell jar for processing and raised fromthe bell jar for loading and unloading of semiconductor substrates.Consequently, the loading of substrates is carried out while thesusceptor is suspended directly over the open mouth of the bell jar.

The gimballed upper support of the susceptor has considerable complianceto permit the susceptor to self-center when it is in the bell jar, suchthat the susceptor can be rotated during processing without significanteccentricity. However, as outlined above, the same compliance comprisesa drawback during the operation of loading and unloading substrates bymeans of a robotic loader. The filtered air stream which is used to aidin the removal of noxious vapors has the additional and unwanted effectof causing the susceptor to swing, making loading of the substratesdifficult.

Accordingly, a susceptor stabilization means in the form of a carriagewhich is movable toward and away from the susceptor carries on its uppersurface a pair of compliant contactor pads for frictionally engaging thelower end of the susceptor. When the carriage has been moved to aposition near the mouth of the bell jar and beneath the susceptor, thecarriage is raised slightly to cause these contactor pads to grip thelower edge of the susceptor, effectively immobilizing it during loading.

The same carriage also incorporates a vacuum duct extending from anopening located on the underside of the carriage, adjacent the mouth ofthe bell jar, to a remotely located source of low vacuum. Consequently,when the carriage is extended into position below the susceptor, theopening on its underside draws noxious and corrosive vapors andparticulate matter from the open mouth of the bell jar.

At the completion of the loading operation, the carriage is withdrawn,permitting the loaded susceptor to be lowered into the bell jar.

BRIEF DESCRIPTION OF THE DRAWING

The above and other features, objects and advantages of the presentinvention, together with the best mode contemplated by the inventorsthereof for carrying out their invention will become more apparent fromreading the following description of embodiments of the invention whilestudying the associated drawing, the various figures of which represent:

FIG. 1 is a side view, partly in elevation and partly in section,illustrating the present invention during the operations of substrateloading and unloading;

FIG. 2 is a detail view, partly broken away, illustrating the gimballedsusceptor mounting used in the present invention;

FIG. 3 is a top view illustrating a susceptor stabilization and noxiousvapor evacuation apparatus useful in the present invention;

FIG. 4 is a side view of the apparatus of FIG. 3.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In FIG. 1, a graphite susceptor 1 is shown as it would appear during theoperation of loading and unloading semiconductor wafers 3. Susceptor 1is, for example, an elongated, five-sided support structure having threewafers 3 retained in correspondingly-shaped recesses on each of itssides. As illustrated, susceptor 1 has a slight axial taper, such thatit is larger at the bottom than at the top. Formed in this way, each ofthe sides of susceptor 1 slopes in a sense to provide a small radiallyinward gravitational force component on each of wafers 3 to preventaccidental dislodging of the wafers during processing.

A support hanger 5, in the form of a short stub shaft, connectssusceptor 1 to a rotatable support structure 7 which can be raised tothe illustrated loading position and lowered to load susceptor 1 into areaction chamber or bell jar 9 for processing. During processing withinbell jar 9, susceptor 1 and wafers 3 are subjected to temperatures inthe region of 1100 to 1200 degrees Celsius in a reactive gaseousenvironment.

In order to ensure that the mixture of gases in contact with each of thewafers is uniform, susceptor 1 is rotated to agitate and stir thegaseous mixture. Such stirring action is effective at maintaining auniform gaseous mixture only if susceptor 1 remains centered such thatits axis coincides with the axis of rotation. Accordingly, supporthanger 5 is supported within support structure 7 in a manner whichprovides considerable compliance, such that susceptor 1 will self-centerby gravitational force as will become clearer from the later discussionof FIG. 2.

Loading of unprocessed substrates and unloading of processed ones iscarried out by a robotic loader 11 which is illustrated somewhatschematically in FIG. 1. Loader 11 is equipped with four fingers 13,only two of which are shown in FIG. 1, for gripping each substrate byits edges.

Loader 11 uses a system of infrared sensors (not shown) in order toaccurately map the locations of each of the three substrates on eachside of susceptor 1. As each of the five sides of susceptor 1 iscompleted, hanger 5 is rotated to access the next side, whereupon loader11 begins the operation of loading by storing data which determines theexact location of each of the three substrates on the side.

Using this stored data, loader 11 can efficiently complete the loadingof all three substrates without pausing to relocate the appropriaterecesses. However, susceptor 1 must remain stationary throughout theloading of each side in order that the location data stored prior toloading remain valid throughout the loading operation.

In accordance with the present invention, susceptor 1 can be maintainedin a fixed position throughout the operation of loading each of itssides by the use of a susceptor stabilizer 15 which can be selectivelyengaged at the start of the loading operation on each side anddisengaged when necessary to rotate susceptor 1.

Stabilizer 15 can be simply and effectively realized in a form whichengages susceptor 1 at its lower edge, as illustrated in FIG. 1. Whenthus engaged, susceptor 1 is supported at widely separated pointslocated at its top and bottom, and is firmly fixed during the loadingoperation.

Although the structure of stabilizer 15 will be fully discussed withrespect to FIGS. 3 and 4, it may be noted here that engagement ofstabilizer 15 with susceptor 1 is accomplished simply by pressing a pairof frictional contactors 17 (only one of which is visible in FIG. 1)firmly against the lower edge of susceptor 1. For this purpose a liftarm 19, raised and lowered by a pneumatic lift cylinder which will bedescribed later with respect to FIG. 4, is used to raise and lowerstabilizer 15 during the loading of susceptor 1.

In FIG. 2, details concerning the mounting of support hanger 5 withinsupport structure 7 are clarified. Support hanger 5 is suspended from adriving shaft 21 by a mounting ring 23 and a pair of trunnion pins 25and 27. Mounting ring 23 and trunnion pins 25 and 27 together form agimballed joint which provides sufficient compliance to accommodate aslight misalignment between shafts 5 and 21, and to thus permitsusceptor 1 to self-center through the action of gravity.

Rotation of susceptor 1 both during processing and during the substrateloading operation is accomplished by rotating shaft 21, such that therotary motion is transmitted through the gimballed joint. However,ensuring that each of the sides of susceptor 1 is correctly orientedfacing the robotic loader 11 of FIG. 1 requires that the location ofthese sides be known in relation to the rotational position of shaft 21.

Accordingly, although not shown in FIG. 2, a second pin, azimuthallydisplaced from pin 25 by an angle which is not 90 degrees, extendsthrough ring 23 and shaft 21 for the purpose of ensuring that susceptor1 can only be mounted with its sides in a preordained orientation.

FIG. 3 illustrates the structure of stabilizer 15 in top view, whileFIG. 4 shows the same structure from the side. A platform 29 ispivotally supported on a pair of upright posts 31 which are joined to abase 33. A stop 35 is also joined to base 33, and serves to limit thedownward pivotal motion of platform 29 to the position illustrated, withplatform 29 parallel to base 33.

A movable shuttle or carriage 36 is supported upon a pair of travelingrods 37 which are in turn supported within four ball slides 39 mountedon platform 29. Carriage 36 is shown extended to the left in FIGS. 1, 3,and 4 as it would be when in use to stabilize susceptor 1. However,carriage 36 is movable to the right as indicated by the phantom outline41 in FIG. 4, such that its full range of motion is as indicated byarrow 43.

A pneumatic cylinder 45 is used to drive carriage 36 either to the leftor right in the drawing by applying air pressure to either of a pair ofair pressure lines 47a or 47b. Similarly, the entire stabilizer assemblyconsisting of platform 29, carriage 36, rods 37, slides 39 and cylinder45 can be raised and lowered by a pneumatic lift cylinder 49 to causecontactor pads 17 to press against the lower edge of susceptor 1.

These horizontal and vertical movements are controlled by automaticallyactuated air pressure valves (not shown) controlled by a computer (notshown) which also sequences the operation of the robotic loader 11. Dataconcerning the horizontal position of carriage 36 is provided by ahorizontal position switch 51 which is indicated schematically in FIG.3. Similarly, data concerning the vertical position of the mechanism isprovided by a vertical position switch 53 which is indicatedschematically in FIG. 4.

Each of switches 51 and 53 is shown coupled to carriage 36 by a dottedline. Whenever carriage 36 is lowered away from susceptor 1, thecontacts of switch 53 are closed. Similarly, whenever carriage 36 iswithdrawn from the region of susceptor 1 (i.e., moved all the way to theright in the figures), the contacts of switch 51 are closed.Accordingly, by sensing the states of switches 51 and 53, the computercan determine when susceptor 1 can safely be rotated to permit accessinga different side thereof.

In order to extract corrosive vapors from the open mouth of bell jar 9when carriage 36 is in its illustrated left position, a remotely locatedvacuum system (not shown) is coupled via a vacuum duct 55 to theunderside of carriage 36. Carriage 36 is formed as a hollow member,having a lower wall identical to the upper wall illustrated in FIG. 3with the exception that the leftmost edge of the lower wall, asindicated by dotted line 57, is undercut to form a downwardly orientedvacuum opening.

Accordingly, carriage 36 serves as a portion of the vacuum duct. Duringthe loading cycle, corrosive vapors and particulate matter within belljar 9 are drawn into carriage 36, through duct 55, and are collected bythe remote vacuum system.

Although this invention has been described with some particularity inreference to embodiments thereof which, taken together, comprise thebest mode known to the inventors thereof for carrying out theirinvention, many changes could be made and many alternative embodimentscould thus be derived without departing from the scope of the invention.Consequently, the scope of the invention is to be determined only fromthe following claims.

We claim:
 1. In a semiconductor-processing apparatus of the typeemploying a reaction chamber for confining a reactive gaseous atmospherein contact with a substrate, the combination comprising:a susceptor forsupporting said substrate; susceptor mounting means for supporting saidsusceptor within said apparatus; a reaction chamber having a closableopening through which said susceptor can be inserted and removed fromsaid chamber; chamber loading means for causing relative motion betweensaid chamber and susceptor along a chamber loading axis between a closedposition in which said susceptor is confined within said chamber duringsubstrate processing, and an open position in which said susceptor iswithdrawn from said chamber through said chamber opening to permitremoval of a processed substrate and loading of an unprocessedsubstrate; and a susceptor stabilization means, independent of thesusceptor mounting means, comprising chamber exhaust means for producinga vacuum in a region adjacent said chamber opening for withdrawingnoxious process-byproduct vapors from said chamber when said closableopening is open.
 2. The apparatus of claim 1 wherein said susceptormounting means suspends said susceptor within said apparatus at an uppersupport point on said susceptor, and wherein:said susceptorstabilization means is mounted on said apparatus and is selectivelyoperable to: (1) move into supporting engagement with said susceptor ata point thereon removed from said upper support point for fixing theposition of said susceptor during the loading and removal of substrates,and (2) move out of supporting engagement with said susceptor.
 3. Theapparatus of claim 1 wherein said susceptor stabilization meanscomprises:a carriage selectively movable along a path of motiongenerally transverse to said chamber loading axis, said path of motionextending from a position adjacent said chamber opening to a positionremoved from said chamber opening; a vacuum duct coupled to saidcarriage for movement therewith along said path of motion, said vacuumduct having an opening adjacent a portion of said carriage facing saidchamber loading axis, and extending from said duct opening to a locationremote from said chamber axis for connection to a source of vacuum. 4.The apparatus of claim 3 wherein:said susceptor stabilization means ismounted on said apparatus and is selectively operable to: (1) move intosupporting engagement with said susceptor for fixing the position ofsaid susceptor during the loading and removal of substrates, and (2)move out of supporting engagement with said susceptor.